WASHINGTON — President Donald Trump announced Monday the U.S. is putting North Korea's "murderous regime" on America's terrorism blacklist, despite questions about Pyongyang's support for international attacks beyond the assassination of its leader's half brother in February.

Trump said the designation of North Korea as a state sponsor of terrorism was long overdue, and he promised a new wave of sanctions as part of a "maximum pressure campaign" over the North's development of nuclear weapons that could soon pose a direct threat to the U.S. mainland.

President Donald Trump announces that the United States will designate North Korea a state sponsor of terrorism during a cabinet meeting at the White House, Monday, Nov. 20, 2017, in Washington. (AP Photo/Evan Vucci)

North Korea will join Iran, Sudan and Syria on the blacklist. The North had been designated for two decades until 2008 when it was removed in a bid to salvage international talks aimed at halting its nuclear efforts. The talks collapsed soon after and haven't been revived since.

The primary impact of the designation may be to compound North Korea's growing international isolation as it is already subject to an array of tough U.S. sanctions restricting trade, foreign assistance, defence sales and exports of sensitive technology. The step is likely to further sour relations between Washington and Pyongyang that have turned uglier with name-calling between Trump and Kim Jong Un.

Spectators listen to a television news brodcast of a statment by North Korean leader Kim Jong-Un, before a public television screen outside the central railway station in Pyongyang on September 22, 2017. ED JONES/AFP/Getty Images

There is strong bipartisan support for the move in Congress, which had passed legislation in August requiring the State Department to make a determination on putting North Korea back on the list.

"In addition to threatening the world by nuclear devastation, North Korea has repeatedly supported acts of international terrorism, including assassinations on foreign soil," Trump said as he announced the designation at a Cabinet meeting at the White House.

However, the action had been debated for months inside the administration, with some officials at the State Department arguing that North Korea did not meet the legal standard to be relisted as a state sponsor of terrorism.

U.S. officials involved in the internal deliberations said there was no debate over whether the slaying of Kim's half brother Kim Jong Nam was a terrorist act. Malaysian authorities have said he was killed by two women who smeared suspected VX nerve agent onto his face at Kuala Lumpur airport Feb. 13.

However, lawyers said there had to be more than one incident, and there was disagreement over whether the treatment of American student Otto Warmbier, who died of injuries suffered in North Korean custody, constituted terrorism.

In this March 16, 2016, file photo, American student Otto Warmbier, center, is escorted at the Supreme Court in Pyongyang, North Korea. (AP Photo/Jon Chol Jin, File)

Neither Trump nor the State Department specified Monday which acts of terrorism and assassination the North had supported. In making the announcement, Trump did refer to Warmbier "and the countless others so brutally affected" by North Korean oppression.

He said more sanctions would be imposed on North Korea and "related persons" that the Treasury Department would begin to announce Tuesday — part of rolling effort to deprive Pyongyang of funds for its nuclear and missile programs and leave it internationally isolated.

"It will be the highest level of sanctions by the time it's finished over a two-week period," Trump said.

In this undated file photo distributed on Saturday, Sept. 16, 2017, by the North Korean government, North Korean leader Kim Jong Un, center, attends what was said to be the test launch of an intermediate range Hwasong-12 missile at an undisclosed location in North Korea. (Korean Central News Agency/Korea News Service via AP, File)

Anthony Ruggiero, a sanctions expert at the Foundation for Defence of Democracies think-tank , said the designation does not grant sanctions authority that the administration does not already have but will help "push additional countries to cut commercial and diplomatic ties with North Korea."

Some analysts have said Pyongyang could use the designation as a pretext for renewed weapons tests after a two-month hiatus. The latest missile test overflew Japan Sept. 15.

House legislation introduced this year had urged the State Department to review a list of purported acts by North Korea, including assassinations of dissidents and weapons sales to militant groups including Hamas and Hezbollah. It requested a determination as to whether such acts constitute support for international terrorism.

The legislation also cited the 2015 computer hack of Sony Pictures Entertainment, which the FBI blamed on North Korea. Hackers threatened movie theatres that screened "The Interview," a comedy parodying the North's leader, Kim.